Have you tried wintergreen oil? You can find it in the health food
section as an essential oil. It also transfers, smells great, and isn't
hazardous. We have used it to transfer Xerox images onto zinc plates
for etching.

Have you tried nail polish remover?
I do a xerox transfer project with my seniors - basically I have a one
page
handout full of a variety of clip art images I have found - we cut out
what
we want to use, and then place face down onto paper, and rub nail polish

remover onto the back - the xerox tranfers quite well.
Different papers react differently of course - some are better than
others.
The photocopy has to be heavy ink, and a lazer image (not ink jet)
Also, the nail polish remover has to be acetone (not the non-acetone
stuff).
I usually get the lemon smelling stuff - hahaha!
Good luck
Sue